C++讀取視頻幀保存成圖片

#include<opencv2\opencv.hpp>
#include <iostream>
#include <stdio.h>
#include<fstream> 

using namespace std;
using namespace cv;



int main()
{
    //打開視頻文件：其實就是建立一個VideoCapture結構  
    VideoCapture capture("D:/MyData/zhaohz4/Desktop/Nansha_video/2.mp4");   
    //檢測是否正常打開:成功打開時，isOpened返回ture  
    if (!capture.isOpened())
        cout << "fail toopen!" << endl;

    //獲取整個幀數  
    long totalFrameNumber = capture.get(CV_CAP_PROP_FRAME_COUNT);
    cout << "整個視頻共" << totalFrameNumber << "幀" << endl;
    //設置開始幀()  
    long frameToStart = 1;
    capture.set(CV_CAP_PROP_POS_FRAMES, frameToStart);
    cout << "從第" << frameToStart << "幀開始讀" << endl;


    //設置結束幀  
    int frameToStop = 4000;

    if (frameToStop < frameToStart)
    {
        cout << "結束幀小於開始幀，程序錯誤，即將退出！" << endl;
        return -1;
    }
    else
    {
        cout << "結束幀為：第" << frameToStop << "幀" << endl;
    }

    //獲取幀率  
    double rate = capture.get(CV_CAP_PROP_FPS);
    cout << "幀率為:" << rate << endl;
    //定義一個用來控制讀取視頻循環結束的變量  
    bool stop = false;

    //承載每一幀的圖像  
    Mat frame;

    //顯示每一幀的窗口  
    namedWindow("Extractedframe");

    //兩幀間的間隔時間:  
    //int delay = 1000/rate;  
    double delay = 2000 / rate;     //??


    //利用while循環讀取幀  
    //currentFrame是在循環體中控制讀取到指定的幀后循環結束的變量  
    long currentFrame = frameToStart;


    //濾波器的核  
    int kernel_size = 3;
    Mat kernel = Mat::ones(kernel_size, kernel_size, CV_32F) / (float)(kernel_size*kernel_size);

    while (!stop)
    {
        //讀取下一幀  
        if (!capture.read(frame))
        {
            cout << "讀取視頻失敗" << endl;
            return -1;
        }
        if (currentFrame % 3 == 0)    //每三幀保存一幀
        {
            cout << "正在讀取第" << currentFrame << "幀" << endl;
            imshow("Extractedframe", frame);

            cout << "正在寫第" << currentFrame << "幀" << endl;
            stringstream str;
            str << "2-"<<currentFrame << ".jpg";     //保存格式
            cout << str.str() << endl;
            imwrite(str.str(), frame);
        }

        //waitKey(intdelay=0)當delay≤ 0時會永遠等待；當delay>0時會等待delay毫秒  
        //當時間結束前沒有按鍵按下時，返回值為-1；否則返回按鍵  
        //int c = waitKey(delay);
        int c = waitKey(1000);
        //按下ESC或者到達指定的結束幀后退出讀取視頻  
        if ((char)c == 27 || currentFrame > frameToStop)
        {
            stop = true;
        }
        //按下按鍵后會停留在當前幀，等待下一次按鍵  
        if (c >= 0)
        {
            waitKey(0);
        }
        currentFrame++;

    }
    //關閉視頻文件  
    capture.release();
    waitKey(0);
    return 0;
}